1. Field of the Invention
The present invention relates to a method for manufacturing a turbine shell for use in a torque convertor.
2. Description of the Related Art
A torque convertor is a mechanism used for power transmission between an engine and a transmission. A torque converter generally includes a front cover and an impeller shell which together define a fluid filled chamber. Impeller blades are fixed to the impeller shell within the fluid filled chamber. A turbine shell and a stator are also disposed within the chamber, both the turbine shell and the stator being relatively rotatable with respect to the front cover and the impeller shell. The turbine shell is disposed within the chamber and arranged to confront with the front cover. The turbine shell is formed with a plurality of turbine blades fixed to one side of the turbine shell facing the impeller blades of the impeller. A turbine hub is fixed to the inner circumferential portion of the turbine shell by rivets. The turbine hub is configured to be connected to the input shaft of the transmission.
Typically, when viewed in cross section, the turbine shell has a curved contour having a concave and arcuate shape. The concave and arcuate shape is necessary for receiving fluid from the impeller. Rotation of the impeller causes fluid in the fluid filled chamber to move toward the turbine shell. In order to efficiently capture and transmit the force of the fluid movement, the concave and arcuate shape of the turbine shell has been developed over the years of torque convertor usage. Further, each turbine blade is curved forming a vane that conforms with the shape of the turbine shell. Specifically, each turbine blade has a first arcuate edge shaped to conform to the concave and arcuate shape of the turbine shell. The first arcuate edge is fixed to the turbine shell. A second arcuate edge of each turbine blade is shaped to receive fluid moved by the impeller. The second arcuate edge faces the impeller. Typically, tabs are formed on the first arcuate edge at three positions of each turbine blade: an inner circumferential portion, an outer circumferential portion and an intermediate portion. The tabs are shaped to extend into slits formed in the turbine shell. The tabs are pressed or deformed after being inserted into the slits.
The turbine shell of the above-described conventional torque convertor is typically manufactured by the following steps. First of all, a flat metal material is punched to form an outer circumferential circle defining a disc shaped member. The disc shaped member is then punched to form an inner circumferential hole in its center. Next, the disc shaped member is deformed by drawing work to have a curved concave shape (when viewed in a side, cross sectional view). Subsequently, a plurality of slits are formed in the curved concave portion. It is necessary to punch out the above described slits after the disc shaped member has been deformed to have the curved concave shape in order to insure that the slits properly align with the tabs on the turbine blades. Specifically, the inner circumferential slits, the outer circumferential slits and the intermediate slits must align with the above described tabs. In order for proper alignment, the slits are formed in stages or steps. The inner circumferential slits are first formed at appropriate positions on the turbine shell while the shell is rotated. Subsequently, the intermediate slits are formed at a plurality of appropriate positions and finally, the outer circumferential slits are formed at a plurality of appropriate positions.
Thus, in the conventional turbine shell manufacturing method, the slits are formed in three separate stages or steps. Consequently, the manufacturing costs are correspondingly high.